This invention deals generally with heat exchangers and more specifically with a device for using cooling fluid such a liquid to remove heat from a small device producing a significant amount of heat.
High power density electronic, optical, and electrical devices are sometimes cooled by attaching them to an exterior surface of a wall of a liquid cooled “cold plate” or heat exchanger, a relatively low height enclosure that has liquid flowing through the volume of the enclosure. The heat flow path in such a system is from the heat source, into and through the wall of the liquid enclosure, and then into the liquid that is flowing through the heat exchanger enclosure.
In order to increase the surface available to transfer heat into the liquid, a heat transfer structure is typically attached to the interior surface of the wall of the heat exchanger enclosure to which the heat source is attached. The main goals of such a heat transfer structure are to increase the area of the heat transfer surfaces between the heat source and the liquid, and to facilitate convective heat transfer between the heat transfer structure and the liquid. Some of the configurations used for heat transfer structures are small channels formed into the inner walls of the heat exchanger enclosure, folded miniature fins, porous structures through which the liquid flows, pin fins protruding from the inner walls of the enclosure, and various flow channel layouts or flow turbulence creating structures.
Regardless of the specific structure, the goals are to minimize the temperature drop between the heat exchanger enclosure inner wall and the thermal transfer structure by having a good thermally conductive bond between them, and to minimize the liquid flow pressure drop while maximizing the heat transfer surfaces between the heat transfer structure and the liquid coolant.
However, because of limited heat conductivity within heat transfer structures the prior art heat transfer structures within enclosures are only effective within a limited region quite close to the heat source. They are not effective in spreading the heat longitudinally along the liquid flow path or laterally in the direction perpendicular to the flow. The regions upstream and downstream of the heat source are much less effective in removing heat because of the longer heat conduction paths to those regions within heat transfer structure. The requirement of heat transfer structures for large surface areas within limited spaces leads to thin structures that limit heat conduction over the longer distances within heat exchanger enclosures.
Most efforts to address this problem have added heat pipes either between the heat source and the envelope or within the wall of the envelope itself. While such approaches are effective in spreading the heat from the heat source over the length and width of the envelope, they have a substantial shortcoming in that the heat pipe is required to transfer the entire heat load. That means the heat pipe is in the main heat transfer path. This places a burden on the heat pipe, and for applications in which the heat pipe and liquid heat transfer coefficients are of the same order of magnitude such structures are less effective because the extra thermal resistance of the heat pipe affects all the heat being moved.
It would be very beneficial to have a cold plate heat exchanger that compensated for the low thermal conductivity of the typical heat transfer structure without the possibility of adding thermal resistance between the heat source and the coolant flow.